1. Field of the Invention
The present invention relates to magneto optical current transducers. In particular, the present invention relates to an improvement in the construction of magneto optical current transducers.
2. Discussion of Background
Magneto optical current transducers have been known for a number of years. These particular devices are very useful in measuring current, especially in high voltage lines such as electrical utility power lines. These devices take advantage of the Faraday effect, in which a magnetic field causes a rotation of the plane of polarization of light passing through magento optical material. The strength of the effect is related to the strength of the magnetic field, which in turn is caused by the electrical current flowing through the power line.
Typically, a magneto optical current transducer comprises a light source, a ring of a magneto optical material, a pair of polarizers, and circuit elements to send the light from the source through one of the light polarizers and into the ring, where the light's polarization is shifted by the magnetic field, and then through the second polarizer to detect the degree of polarity shift and analyze it. Examples of such devices are taught by Feldtkeller in U.S. Pat. No. 3,906,343 and Matsumoto in U.S. Pat. No 4,539,521.
The problem with magento optical current transducers is their accuracy. There are several sources of error traceable to birefringence in the glass sensor of the transducer. Birefringence is defined as the splitting of a beam of light into two components that each travel at a different speed. Birefringence can result from the construction of the device and from thermal transients. Both may result in stresses in the magento optical material that will result in birefringence.
The value of accuracy in current measurement cannot be overstated. The current and voltage--both of which can be measured by magneto optical current transducers--relate to energy supplied and billing for electric power service. They can reflect the electrical load used by customers. If electrical power is wheeled from utility service district to service district accounting for its value requires careful measurement.
There remains a need for better magneto optical current transducers.